Telephone system



10 l94: M V955 i 2,214,213

TELEPHONE SYSTEM Filed June 25, 1938 J7 Shets-Shee 2 INVENTOR 1:1 hf! l'i. Vm 5 s ATTORNEYS S 5 O V. H im TELEPHONE SYSTEM Filed June 25. 1938 Sheets-Sheet 3 ATTORNEYS Sem. w, w40. J. H. Voss TELEPHONE SYSTEM Filed June 25, 1938 'i smtssheet. 4

INVENTOR. Jul-m HV1: ss Bmw, MJMMM ATTORNEYS 'Sept 10, l940 J. H. Voss TELEPHONE SYSTEM Filed June 25, 19258 '7- Sheets-Sheet 5 INVENTOR. J c1 [1n H Vn 55 BY m l MM NJA@ ATTORNEYS Sept. l0, 1940.

J. H. VOSS TELEPHONE SYSTEM Filed June 2.5. 193B v snntsfsn-eer, e

ATTORNEY.

Sept. l0, 1940. J. H. Voss TELEPHONE SYSTEM T0 FIG. 7

INVENTOR. Jahn H. Voss BY SAM/l, M 1

ATTORNEYS Patented Sept. l0, 1940 UNITED STATES 2,214,213 TELEPHONE SYSTEM John Henry Voss,

Downers Grove, Ill., assigner to Associated Electric Laboratories, Inc., Chicago, IIL, a corporation of Delaware Application June 25, 1938, Serial No. 215,786

26 Claims.

automatic exchange to an operators position in a distant manual otlice.

matic substation may, by performing a connection release operation, control a supervisory signal device provided at the operators telephone station when a connection between the automatic substation and the operators telephone station is established.

It is an additional object oi the invention to provide, in an automatic telephone system, an improved arrangement, operative when a call is originated at a telephone substation of the paystation type, for transmitting a signal identifying the character of the calling substation to an operators position or telephone station on a call routed by way of the operators position.

It is a still further object of the invention to provide, in a repeater associated with a trunk line extending between an automatic exchange and an operators position in another exchange, an improved circuit arrangement for: transmitting ringing current to the operators telephone station to energize the signal device thereat, transmitting a paystation signal to the operator in the event a call intended for the operators position is originated at a telephone station of the paystation type, and controlling a supervisory signal device located at the operators position.

It is a further and more speciiic object of the invention to provide in a telphone system, a repeater associated with a trunk line extending between two automatic exchanges, which repeater, in conjunction with a repeater asociated with a trunk line extending between one of the automatic exchanges and an operators position in a distant manual exchange, is operative in an improved manner to transmit paystation tone signals to the operators position on calls originating at paystations and to control a supervisory signal device located at the operators position.

(ci. 179-27) l 'I'he invention is illustrated as being incorported in a telephone system wherein two manual oiiices and two automatic interconnected by sociated repeaters so that connections may be established between any pair of lines of the system irrespective of which of the exchanges terminates the calling and called lines of a desiredv connection. The automatic switching equipment provided in each of the two automatic exchanges is diagrammatically illustrated as being of the character disclosed and claimed in applicants copending application Serial No. 189,121; filed February 7, 1938. 'I'he arrangement is such that, when a call, originated at a telephone station of the paystation type associated with a line terminating in one of the automatic exchanges and intended for a substation associated with a line terminating at one of the manual exchanges, is routed through the automatic switching equipment provided in the automatic exchange and over a trunk line to an operators position in the manual exchange, the connection thus established comprises a talking circuit between the calling substation and the operators position which is adapted to be completed in response to the operation of a relay which operates when the call is answered at the operators telephone station. In accordance with one feature of the present invention, means operative in response to the operation of the above-mentioned relay are provided for transmitting a signal to the operators position indicating that a call originates at a telephone station of the paystation type. In the event the connection is routed by way of two of the automatic exchanges to the operators position in the manual ofiice, the established connection comprises a pair of repeaters connected in tandem, the flrst being associated with the trunk line extending between the two automatic exchanges, and the second being associated with the trunk line extending between the second automatic exchange and the distant manual cnice. As thus established, the connection comprises a first loop circuit extending between the two operated repeaters and a second loop circuit extending to the operators telephone station, which second loop circuit is completed through operation of the abovementioned relay when the call is answered by the operator. In accordance with a further feature oi' the invention, means responsive to the operation of the relay are provided, for interrupting the rst loop circuit, and means, in-

cluded in the first of the tandem connected repeaters and operative in response to the interruption of the first loop circuit, are provided for impressing a signal on the second loop circuit indicating that the call originates at a telephone station of the paystation type. A further feature of the invention pertains to the particular arrangement for projecting a splash of ringing current over a trunk line to energize the signal device provided at an operators position at one of the manual offices. More particularly, this arrangement includes a ringing relay embodied in the repeater associated with the trunk line extending to the operators position and operative in response to the seizure of the repeater to connect the ringing-current source to the trunk line, therebyto energize the signal device at the operators position. A ring cutoil relay is also provided, which ring cutoff relay includes a pair of windings, one of which is included in an operating circuit for the ring cutoff relay and is energized over this circuit from the ringing-current source in response to the operation of the ringing relay. The other winding of the ring cutoff relay is included in a holding circuit for the lastmentioned relay, which holding circuit is completed in response to the operation of the ring cutoff relay. The ring cutoff relay also includes contacts for opening the operating circuit of the ringing relay, thereby to arrest the ringing operation in response to the operation of the ring cutoff relay.

In accordance with a further feature of the invention, the supervisory signal device provided at the operators position in one of the manual offices is arranged to be controlled in an improved manner by apparatus provided in the repeater associated with the trunk line by way of which connections are routed to the operators position. This feature of the `invention is directed to the provision of apparatus operative when a connection between an automatic substation and the operators position is fully completed, for preventing the release of the operated switch train in response to a release operation performed at the automatic substation together with means responsive to repeated release operations performed at the automatic substation for repeatedly completing the operating circuit for the supervisory signal device. More particularly, the supervisory signal device provided at the operators position includes an operating circuit which is arranged to be completed in response to the operation of a relay provided at the operators position. The last-mentioned relay includes a winding which is arranged to be energized by way of a circuit including a winding of a second relay provided in the repeater associated with the trunk line extending to the operators position. There is also provided an impedance element in the form of a second high resistance winding of the second relay whichis adapted to be serially included in the operating circuit for the first relay. The impedance and, more particularly, the resistance, of this second winding is so proportioned relative to the impedances or resistances of the other relay windings that the relay which controls the signal device is operated only when the second winding of the second relay is excluded from its energizing circuit. For the purpose of controlling the operation of the signal device control relay, there is provided in the repeater, means, controllable from a substation included in a connection established to the operators position, for selectively including the second winding of the second relay in the operating circuit for the signal device control relay.

Further features of the invention pertain-to the particular arrangement of the circuit elements whereby the above and additional operating features are attained.

The novel features believed to be characteristic of the invention are set forth with partlcularity in the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification, taken in connection with the accompanying drawings in which Figure 1 illustrates the general arrangement of a system having the above-outlined features of the invention incorporated therein, Figs. 2, 3, 4, 5, 'l and 8 illustrate the circuit arrangement of certain of the apparatus embodied in the system of Fig. 1, and Fig. 6 illustrates the mode of combining Figs. 2, 3, 4, 5, 'l and 8 to form a unied system.

Referring now to the drawings, the system there snown comprises two small community automatic exchanges I0 and 30 and two manual offices I5 and 40 arranged to be interconnected by two-way trunk lines, each having associated therewith one or more repeaters constructed and arranged in accordance with the present invention. More particularly, there is provided a group of trunk lines, one of which is indicated at I2, extending between the manual office I5 and the automatic exchange I0; and a second group of trunk lines, one of which is indicated at I3,

extending between the automatic exchanges I0 and 30. A third group of trunk lines including the line is provided, the lines of which extend between the automatic exchange 30 and the manual ofilce 40. Each of the enumerated-ex changes I0, I5, 30 and 40 also has extending thereto a plurality of subscribers lines, one of which is indicated at II as extending from the substation A to the exchange III, and a second of which is indicated at I6 as extending from the substation B to the exchange 30. Each o1 these lines may be of the single or multi-party type, as desired.

The switching apparatus provided in the two automatic exchanges I0 and 30 is preferably identical in character, this apparatus being of the particular arrangement disclosed and claimed in the above-referred-to copending application Serial No. 189,121. In brief this apparatus, which, in its embodiment in the exchange I0, is diagrammatically illustrated in Figs. 1 and 5J comprises a plurality of flnder-connector links, each comprising a finder switch and a connector switch of the all-relay type, at which the lines extending to the exchange I0 terminate. Thus, the line II is connected by Way of a line circuit 2l to the contact springs of two of the group relays embodied, respectively, in a finder switch 2l and a connector switch 28 forming one finderconnector link. The line circuit 2| also includes control circuit conductors extending to the distributor and common equipment 25', which equipment is provided for the purpose of assigning links to successive calling lines in a definite order and for causing the finder portion of an assigned link to seize a calling line. Similarly,

the trunk line I2, which extends to an operators position 200 located in the manual oflice I5, is arranged to be connected by way of a two-way repeater 25 and a link line 468 to certain of the contact springs controlled by group relays respectively provided in each of the two switches including the conductors last-mentioned trunk line u and 2s. 'menne circuit fer-the trunk une lz is incorporated in 'and forms a part of the repeater-'25, 'this line circuit being connected and arranged'to control start circuits extending to the distributor and common equipment 25' and C465 to C2461, inclusive. Again, the trunk line I3 extending between the exchange 30 and the exchange I0 is connected by way of a two-way repeater and a link line 190 to. the contact springs controlled by other group relays respectively provided in the finder switch 24 .and the connector switch 26. The is also connected by way of a two-way repeater 885, which is.in all respects identical with the repeater 20, to the automatic switching equipment embodied inthe exchange 30.

The finder switches of the various links embodied in the exchanges I0 and 30 are of the allrelay type andare fully directive in character; that is, all line hunting operations are eliminated through an arrangement wherein only selected ones of' the group'and unit relays are caused to operate when a link is taken for use. The distributor and common equipment is also of the al1-relay type. auxiliary group and unit relays being provided therein which respectively correspond to the group and unit relays embodied in each of the associated finder switches. Each of the connector switches has embodied therein a group of impulse counting relays which function to control the connector group and unit relays during the operation of the connector portion of the link to select a desired line. The arrangement of the connector switches is such that bridged or divided code ringing may be utilized in signalinga desired substation on any selected called line, it being pointed out in this respect that the majority of the lines terminating at the small exchanges I 0 and 30 are expected to be of the party line type. In the operation of each connector switch, four digits are necessary in order to select thedesired type of ringing and the code of the ringing current and to select the desired line; the first digit being utilized to select a trunk line on a trunk call and to select the type of ringing and partially to select the code of the ringing current on a subscriber line call; the

` second digit being utilized to select for operation the group relay associated with the group or lines including the called line; the third digit being utilized to select the particular unit relay corresponding to the desired called line; and the fourth digit beingr utilized nally to select the code of the ringing current and to determine the side of the line over which the ringing current is to be projected, provided divided ringing is to be used in signaling the called substation. The links embodied in the exchange I0 also have associated therewith the usual auxiliary equipment indicated at 21, this equipment comprising apparatus for generating busy and dial-tone voltages, ringing apparatus and a ringing current code interrupter, and timing apparatus arranged to be used in releasing links assigned' to faulty lines or lines having a permanent calling condi-' tion thereon.

Considering brieiiy the operation of the switching apparatus embodied in the exchange I 0, when a subscriber, such, for example, as the subscriber at the telephone A, initiates a call over the line I I to a second subscribers telephone by lifting his receiver from its hook, the line circuit 2| operates to cause the finder-connector link previously assigned by the distributor to the calling line to portion 26 of the link.

be started in operation to seize the calling line. Assuming that the link 24, 261s delegated by the distributor to set up the connection, the iinder portion 24 of the link operates to select the calling line and to connect it through to-the conductors of the link line incoming to the connector More particularly.- when the line circuit operates, the auxiliary group and subgroup relays corresponding to the calling line and embodied in the distributor and common equipment 25' are caused to operate, together with certain of the relays embodied in the allotter or distributor, and, upon operating, cause the operation ofthe corresponding groupand unit relays embodied in the finder portion 24 of the link.

When the calling hne II is seized by the finder switch 24 and extended by way of this switch through the operation of the group and unit relays to the associated connector switch 26, it is marked as busy in all of the other connector switches, and the control equipment of the seized link is automatically conditioned to respond to the impulses of the first series of impulses dialed at the impulsing device conventionally provided at the substation A. During theimpulses of each series, the counting relays embodied therein respond in succession so that, at the end of the series, the particular relay corresponding to the number of impulses making up the series is left operated. At the end of the rst series of lmpulses, the control apparatus of the link operates to determine the type of ringing to be utilized in signaling the desired substation and partially to select the code of the ringing current, providing the number of impulses making up the digit indicates that the call is to be routed to another subscribers line terminating at the exchange I0. On the other hand, if the number of impulses making up the iirst digit indicates that the call is to be forwarded by way of one of the trunk lines extending to the matic exchange 30, the control apparatus embodied in the switch automatically operates, at the end of the digit, to switch the calling loop circuit through to the repeater associated' with an idle trunk of the selected group. In this regard, it is mentioned that the trunk selecting apparatus associated with the links is of a character such that an idle trunk of a selected group is made available immediately a previously assigned trunk is taken for use. Obviously, if the call initiated at the substation no further operation of the apparatus occurs following the trunk selecting operation of the connector switch 26 until the connection is released. If, on the other hand, the connection is to be routed to another subscribers line terminating at the exchange I0, three additional digits are dialed, the arrangement being such that, at the end of the second digit, the particular group relay embodied in the connector switch 26 corresponding to the group of lines including the called line, is caused to operate. Similarly, at the end of the third digit, the particular unit relay embodied in the connector switch 26 is caused to operate. Thus, the desired called line is fully selected. The impulses of the fourth digit, as indicated above, cause the control apparatus of the operated link t operate iinally to select the code of the ringing current and the side of the selected line over which the ringing current is to be projected provided divided ringing is the type of ringing selected in response to the impulses of the first digit.

When the called line is selected, the control A is a trunk call,A

manual office I5 or to the autoapparatus of the operated linkfunctions to test the line for the purpose ofdetermining the busy or idle condition thereof; If the called line is busy, busy-tone current, as generated by a portion of the apparatus 21, is not returned over the loop extending to the calling subscrlber's substation until after the fourth or code selecting digit is dialed at the calling substation. At the conclusion of his digit and if the called line is busy, busy-tone current is returned over the -loop to indicate to the calling party that the desired connection cannot immediately be completed. On the other hand, if the called line is idle at the time it is selected, ringing current of the selected code corresponding to the desired called substation is projected over the called line for the purpose of energizing the signal device provided at the called substation. During the ringing operation, ring-back-tone current is applied Y to the loop extending to the calling substation to indicate to the calling party that the desired substation is being signaled. Finally, the connection between the calling and called substations is completed when the call is answered at the called substation. The arrangementof the link circuit apparatus is such that release of the link utilized in setting up the desired connection between two lines terminating at the exchange I is under the control of the calling party. More particularly, the operated switch train is released in response to a release operation performed at the calling substation.

Referring now in greater detail to the apparatus provided at the operators position 200 and the apparatus embodied in each of the repeaters 20, 25, 885 and 880, and considering first the line terminating apparatus provided at the operators position 200, it is pointed out that the trunk line I2 extends to one side of a repeating transformer 250, the other side of which is connected to the springs of an answer jack 20|. A dialing or calling jack 203 is also provided which is arranged to receive'a plug 208 having its ring and tip contacts connected to the impulsing and shunt springs of a dial-controlled impulsing device s204 of conventional construction and arrangement in the manner illustrated. For the purpose of signaling the operator on calls incoming to the operatorsp'osition 200, there is provided a signal device in the form of a drop 202 which is arranged to be energized by ringing current projected over the trunk line I2 and traversing a condenser 225 connected in series with the energizing winding of the drop. In order to indicate the condition of connections routed by way of the operators position 200, there is provided a supervisory signal device in the form of a lamp 205 which is arranged to be controlled by three relays R2120, R230 and R240. Of the three enumerated relays, the relay R220 is arranged to be energized when an answer or line connecting plug is inserted in the jack 20| and is operative to prepare the operating circuit for the lamp 205, to open the circuit for energizing the drop 202, and to complete a circuit,

described hereinafter, for energizing the control relay R230, which' latter relay is of the marginal type. The relay R240 is provided for the purpose of completing an impulsing circuit extending to the repeater 25 and traced hereinafter, this relay being arranged to be energized only during operation of the impulsing device 204 or, more particularly, in response to closure of the shunt springs 238 embodied in the impulsing device 204.

the manner described hereinafter.

Referring now in greater detail to the repeater 25 illustrated in Figs. 3 and 4, this repeater includes a repeating transformer 300 having ,one

`side at which the endy of the trunk line I2 extending to the exchange I0 terminates and another side arranged to be connected by way of the link line 488 to the contact springs of certain of the group relays embodied in the finder and connector switches forming the automatic switching equipment of the exchange. This repeater also includes nine relays illustrated in Fig. 3 and six relays illustrated in Fig. 4. Of the relays illustrated in Fig. 3, the two relays R300 and R305 are arranged to control the application of ringing current to the trunk line I2 on a call extended to the operators position 200 and operate in an improved manner described more particularly hereinafter. The relay R3l0, which includes two windings, is, in effect, a line relay controllable from the operators position 200 and arranged to have one or both of its windings energized in series with the winding of the marginal vrelay R230. The lower winding of R8I0 is in effect an impedance element which is arranged selectively to be included in the series circuit by way of which the winding of R230 is energized. I'he impedance of the lower winding of R3l0 is so proportioned relative to`the impedance of the winding of R230 and the impedance of the upper winding of R3l0 that R230 operates only when the lower winding of R3l0 is excluded from the series circuit for energizing R3l0 and R280. For the purpose of selectively including one or both of the two windings of R3 I 0 in the series circuit for energizing this relay and R230, there is provided a relay R3I5 which is controllable by way of a connection extended to the operators position 200. More particularly, the relay R3|5 is arranged to be energized in response to the operation of either of two bridging relays R320 and R345, the first of which is of the polarized type and operates only when its two windings are cumulatively energized. The slow-acting relay R325 is provided for the purpose of shunting the series path including the winding 354 of the transformer 350, the upper series of impulses transmitted from the operators position 200, thereby to reduce the resistance of an established loop -circuit extending to an operated one of the connector switches in the exchange I0 during a dialing operation. The relay R330 is operative in response to the seizure of the link line 468 by one of the connector switches embodied in the exchange I0 and functions as a line switching and control relay in The slowacting relay R340, which is under the'control of the relay R345, is provided for the purpose of initiating the operation of the ringing apparatus and for the further purpose of completing a. circuit, traced hereinafter, for impressing ringing voltage on a calling loop circuit extending to a calling automatic substation. Of the relays illustrated in Fig. 4, the relay R400 is provided for the purpose of controlling the cutoil and line switching relay R450 and for the additional purposes of removing ground from the ringing apwinding of R320, and the resistor 3 I 9 during each utor and common equipment 25', andto cause a pay station-.tone signal to be transmitted to the operatorsfposition 200 on calls incoming to this position ,and originating at telephone stations of the paystation type. More particularly, the relay R430 ls operative, when a call originating at a paystation is answered at the operators position 200, to cause the signal to be transmitted to the operators position, and the slow-to-operate relay R440, -which operates a predetermined time interval after the operation of R430, is arranged. to terminate the signal. I'he relay R430, in combination with the slow-to-operate relay R450, also functions momentarily to interrupt an established loop circuit extending to the repeating transformer 350 for the purpose of causing a preceding repeater ofthe character illustrated in Figs. 7 and 8 to transmit a paystationtone signal to the operators position 200 on calls originated at paystations and routed by way of the two automatic exchanges I0 and 30 to the operators position 200. The paystation-tone signal voltage is impressed between the control conductor of the link line 468 and ground on calls originating at telephone stations of the paystation type and associated with lines terminating at the exchange I0. This voltage is, through the operation of the relay R4I0, impressed upon the input terminals of a coupling device in the form of a transformer 420 having output terminals arranged to be connected across the line conductors of the link line 468 when the relay R430 occupies its operated position. For the purpose of balancing the impedances associated with an established talking circuit when the relay R345 is connected to be energized over a loop extending to the repeating transformer 350, there is provided an impedance element 408 having impedance characteristics substantially identical with those of the winding of R345.

Referring now in greater detail to the repeater 20, illustrated in Figs. '1 and 8, this repeater comprises a repeating transformer 800 having one side terminating the conductors of the trunk line I3 and the other side arranged to be connected by way of the conductors of va link line 190 to certain of the contact springs of certain of the group relays respectively embodied in each of the finder and connector switches located in the exchange I 0. The relay and control equipment included in this repeater comprises two rey lays R104 and R100 which are operative to transmit a paystation signal by way of the trunk line I3 to the operators position 895 on calls originating at telephone stations of the paystation type associated with lines extending to the exchange I0 and routed to this operators position. The paystation-tone voltage which appears between the control conductor of the link line 190 and ground is impressed on the line conductors of the trunk line I3 through the provision of a coupling device in the form of a transformer,

103, which corresponds to the coupling device 420 shown in Fig. 4. There is also included in the control equipment a line relay R which operates when connections are routed by way of the trunk line I3 to the exchange I0 and functions to complete start circuits, described hereinafter, extending to the distributor and `common equipment 25'. -These start circuits are arranged to be interrupted through the provision of a slow-to-release cutoff relay R120 which is controlled by a line switching relay R1I0 operative when the repeater 20 is -seized by a connector switch located in the exchange I0. The

relay R150 is also operative inresponse to the seizure of the link line 190 by one of the connector switches provided in the exchange I0 and functions to condition the remaining relay equipment to extend the calling loop circuit .to the repeating transformer 800. The bridging relays R and R135 are arranged to be energized in series over aA loop circuit exten to the repeating transformer 800 and are arr nged respectively to control the battery reversing relay R and the pulsing relay R840- The battery reversing relay is also controlled by a relay R120 which is a slave to the slow-acting relay R8 5.

The relay R840 is arranged to control a slow acting relay R820 which, in turn, controls the operating circuit for a second slow-acting hold relay R830. The second slow-acting relay R830 is also arranged to be controlled by a relay R810. The relay R840 is also included in an impulse correcting network comprising two additional relays R850 and R850, the last-mentioned of which functions to repeat impulses by way of the trunk line I3 to the automatic switching equipment provided in the exchange 30. For the purpose of reducing the impedance of an established impulsing Vcircuit extending. by way of this trunk line, there is provided a slow-acting relay R855 which is arranged to shunt the line terminals of the windings 803 and 804 included in the repeating transformer 800 during each series of impulses. The relay R865 also operates to shunt the winding of the relay R130, included in the calling loop circuit, during yimpulsing. The two relays R8I0 and R8I5 are bridging relays and include windings arranged to be energized in series over an established loop circuitY extending by way of the trunk line I3. More particularly, the relay R8I5 is of the polarized type, such that it only operates when its two windings are cumulatively energized. It is noted that, after a connection is extended by way of the repeater illustrated in Figs. 'I and 8 to an operators position in the distant manual office 40, the relay R8I0 restores each time the established loop circuit to the operators position is interrupted. Thus, this relay is arranged to respond to the momentary interruption of the loop circuit occurring when the operator at the distant operators position answers and functions to control the relay R104, which latter relay is operative to cause a paystation-tone signal voltage to be impressed between the conductors of the link line 190. In order to prevent the relay R104 from being energized during the dialing operation, or in other instances when the loop circuit over which the relay R8I0 is energized, is interrupted, the two slow-to-release relays R815 and R880 are provided, each of which includes contacts for opening the operating circuit for R104.

Referring now more particularly to the operation of the repeater 25 shown in Figs. 3 and 4 to route a connection from the manual oice I5 to one of the lines extending to the automatic exchange I0 on a call initiated at or routed by way of the operators position 200, it is pointed out that the operation of the repeater is started when the operator inserts the plug terminating her telephone set in the jack 20|, thereby to connect the line conductors of the cord extending to the operators telephone set by way of the springs 221 and 229, respectively, to opposite terminals of the winding 25| of the repeating transformer 250. At the springs 228, an obvious circuit is completed for energizing R220, which relay, upon operating, prepares, at RA22I, a circuit for energizing the vsignal lamp 205 and completes, at RA222 and RC223, a circuit for energizing the winding of R230 in series with the upper winding of R3I0 embodied in the repeater 25. The last-mentioned circuit extends from ground at the upper terminal of the winding of R230 by way of this winding, RC223, RA222, RC244 and RA243, where it divides into two branches; one extending by way of the winding 254, C201 and the winding 352; .and the other extending by way of the winding 253, C203 and the winding 35|. From the junction point between the windings `35| and 352, this circuit extends by way of RA305, the resistor 303, RA3I1, RC3I3 and the upper winding of R3I0 to battery.

When energized over the above-traced circuit, the

two relays R230 and R3 I 0 operate, the first thereof completing, at RA23I, the above-mentioned circuit for energizing the signal lamp 205, and the second relay, R3I0 preparing, at RA3I I, a loop l circuit extending to the switching apparatus provided in the exchange I3. At RA3I2 and- RC3I4, the relay R3I0 completes a circuit extending by way of C363 for energizing the slow-acting relay R4I0.

When the relay R4I0 operates, it` completes, at RA4I I, a circuit extending by way of C363 for energizing the lower winding of the polarized relay R320. The relay R320 does not operate when its lower winding is alone energized, this relay being so constructed and arranged that it operates only when both of its windings are cumulatively energized. At RA4I2, the relay R4I0, upon operating, prepares a circuit, traced hereinafter, for energizing the slow-acting relay R325. At RAM3 and RC4I5, the relay R4I0 opens a point in the circuit, traced hereinafter, for energizing the switching relay R330 and, at RA4I3 and RC4I4, the relay R4I0 completes a path for applying ground to the control conductor C361, thereby to mark the trunk line I 2 as`busy in the connector switches to which the conductors C353, C462 and C361 of the link line 463 terminate. This marking path extends from ground at the right terminal of the lower winding of the impedance element 420 by way of this lower winding, RC4I4, andRA4I3 -to the control conductor noted. It is pointed out that, through the operation of R4I0, the trunk line I2 is marked busy to guard against the seizure thereof by one of the numerical switches provided in the exchange I0, immediately the call is initiated at the operators position 200. Thus, the trunk line I2 is guarded against seizure during the period when one of the non-numerical switches provided in the exchange I0 is operating to seize the link line 468.

At RA4 I 6, the relay R4 I 0 completes circuits for respectively energizing the relays R400 and R430. 'I'he rst of these circuits extends from ground at RA4I6 by way of RC405, RA404 and the winding `of R400 to battery, and the circuit for energizing R430 extends from ground at RA4I6 and through the winding of R430 to battery. When the two relays R400 and R430 operate, a holding circuit for R400 is completed, which circuit extends from ground at RA435 by way of RA403, RA404 and the winding of R400 to battery. At RA40I, the relay R400, upon operating, opens a point in the path, traced hereinafter, for connecting the ringing-tone voltage source to the line conductor C353, and, at RA406, the relay R400 completes a path extending by way of -RC401 and RA453 for applying ground to the tone apparatus start conductor C463, thereby to initiate the operation of this apparatus in a well-known manner. At RA402, the relay R400 prepares a point in the cir- :Izel'litl traced hereinafter, for energizing the relay The relay R430, upon operating, moves its armature RA433 into engagement with the associated weighted armature RA434. When RA433 strikes the contact carried by RA434, the lastmentioned armature starts to vibrate, alternatively to make andv break contact with-RA433. As shown, these two armatures are included in the operating circuit for the relay R440, which relay, due toits slow-to-operate characteristic, does not operate for a time interval required for RA434 to settle into resting engagement with RA433. At RA4 42 and RA445 and their respective associated contacts RC443 and RC446, the relay R440, upon operating, opens two points in the path, traced hereinafter, for impressing a paystation-tone voltage on the loop, including the trunk line I2 and extending to the operators position 200. At RA441, the relay R440 opens a point in an alternative path, traced hereinafter, for applying ground to the tone apparatus start conductor C463.

At RA43I the relay R430, upon operating, completes an obvious circuit for energizing the slowto-operate relay R430,which latter relay, upon operating, prepares, at RA46I, a loop circuit which is described hereinafter. At RA436, the relay R430 applies ground to the tens relay control conductor C465, which conductor is included in the operating circuit for the one of the tens or group relays provided in the distributor 25' corresponding to the group of lines including the link line 453. At RA431, the relay R430 connects the startconductorC461 to the unit relay control conductor C466, thereby to prepare the operating cir-l cuit for the particular unit relay provided in the 1dnilstrlliutor 25' which corresponds to the trunk As explained in the above-referred to copending application Serial No. 189,121, when ground is applied to the tens relay start conductor C465 and the start conductor C461 is connected to the unit relay control conductor C466, the group or tens relay provided in the distributor 25', corresponding to the particular group of lines including the link line 463, and the particular un'it relay corresponding to this trunk line are caused to operate to initiate the operation of a previously assigned finder switch to seize the linkv line 463, providing an idle hurler-connector link is available. l

The apparatus included in the distributor and common equipment 25 is so .arranged that, in the event all of the links having access to the link line 463 are busy at the time the calling condition is created on the trunk line l2, busytone voltage is impressed between the all-linksbusy conductor C464 and ground. Thus, if all of the links provided in the exchange I0 and having access to the link line 463 are busy, a circuit is completed immediately the relay R3I0 operates lfor causing a busy-tone signal to be transmitted by way of the trunk line I2 to the operators position 200. The path of the busytone current extends from the ungrounded terminal of the busy-tone source by way of C464, the condenser 469, RA454, C353, RA3II, C356, the winding 353,l the condenser 353', the winding 354, C351 and RA452 to the grounded terminal of the busy-tone source at RC453. 'I'he alternating busy current flowing over the circuit just traced causes a corresponding induced voltage to be developed between the terminals o1' the series connected repeating transformer wind--v ings 35| and 352, which voltage is impressed by means comprising the trunk line I2 and the transformer 250 between the terminals of the receiver embodied in the operators telephone set. 'Ihe resulting operation of the operators receiver indicates that the desired connection can not immediately be established.

Assuming that the finder-connector link 24, 26 provided in the exchange I0 is idle at the time the call is initiated at the operators position 200 and, further, that this link is the link which has been previously assigned by the distributor and common equipment to the use of the call, when the group and units relays provided in the distributor 25 operate, the finder portion 24 of the assigned link is set in operation to seize the link line 468. More particularly, the group and unit relays provided in the switch 24 and 'corresponding to the operated group and unit relays in the distributor 25 are caused to operate to connect the conductors of the link line 468 through to the trunk extending to the connector switch 26. As explained in the above-referred to copending application, when the line 468 is seized by the finder switch 24 and switched through to the connector switoi 26, certain of the relays provided in the connector switch 26 are caused to operate to apply ground potential to one of the line conductors of the trunk line incoming to the switch 26, which one line conductor is, following the complete operation of the nder switch 24, connected to the line conductor C462 of the link line 468. When ground is applied to C462, the relay R450 is energized over a circuit extending by Way of this grounded conductor. RA402, RC451, RA456 and the winding of R450 to battery. Upon operating, the relay R450 completes a holding circuit for itself, this circuit extending from ground at RA435 by way of RA455, RA458 and the winding of R450 to battery. At RA456 and RC451, the relay R450 opens a point in its operating circuit, as traced above. At RA454, the relay R450 open a point in the circuit, traced previously, traversed by the busy-tone current and completed when an al1- links-busy condition prevails in the exchange I0.

At RA45I and RA452, the relay R450 completes the above-mentioned loop circuit extending from the repeating transformer 350 by way of the link line 460 and the operated iinder switch 24 to the connector switch 26, thereby to provide a holding circuit for the line relays embodied in this connector switch. This loop circuit may be partially traced as extending by way of C358, RASII, C356, the winding 353, RA333, RC334, 'the upper winding of R320, the resistor 3| 9, the winding 354, C351, RA452 and RA45I to C462. It will be understood that one or more of the respective windings of the two line relays provided in the connector switch 26 are energized in series with the upper winding of R320 when the abovementioned and partially traced loop circuit is completed. The polarity of the current traversing this circuit is such-that the upper and lower windings of R320 are differentially energized. Thusthe relay R320 is not caused to operate at this time.

At RA458, the relay R450, upon operating, interrupts the above-traced path for applying ground to the tone apparatus start conductor C463. At RA459, the relay R450 opens a point in the above-traced path for applying ground to the tens relay control conductor C465 and, at RA459', the relay R450 opens a point in the path for connecting the start conductor C461 to the units relay control conductor C466'. When ground is removed from C465 and the start conductor C461 is disconnected from C466, the distrlbutor and common equipment 25' are released for use in connection with other calls, it being pointed out that this apparatus operates to assign another idle link for use on the next succeeding call immediately the link 24, 26 becomes busy.

Following the operation of the nder switch 24 to seize the link line 468 and the operation of the relay R450 to extend the above-traced loop circuit from the repeating transformer 350 to the operated connector switch 26, ground. is returned through the operated finder switch 24 to the control conductor C361 to maintain the line 460 marked as busy, and the connector switch is conditioned to respond to the impulses making up the digits dialed at the operators position 200. In this regard, it is noted that, when the loop circuit is extended to the connector switch 26, dial tone is returned over the loop and by way of the trunk line I2 to the operators telephone to indicate that the dialing operation may be started. Upon receiving dial tone, the operator inserts the plug 208 in the jack 203 and operates the dial controlled inpulsing device 204 in accordance with the directory number identifying the desired line. If, for example, the line Il extending to the substation A is being called, a four-digit number identifying the called line and the ringing code of the called substation A is dialed at the operators position 200. D uring each series of impulses dialed at the operators position 200, the shunt springs 238 embodied in the impulsing device 204 are closed to complete a circuit extending by way of the jack spring 235 for energizing the relay R240. 'Ihis circuit is held completed at the shunt springs 238 throughout each series of impulses. The relay R240, upon operating, interrupts, at RA243 and RC244, the above-traced series circuit including the winding of R230 and the upper winding of R3I0. At RA242 'and RA243, the relay R240 completes an alternative circuit extending by way of the impulsing springs 231 and the jack spring 234 for holding the relay R3|0 operated. At RA24I, the relay R240 completes an obvious alternative circuit for maintaining the signal lamp 205 energized so that, when R230 restores, shortly after the operation of R240, to open the original operating circuit for the lamp 205, the illuminated condition of this lamp is not disturbed. During each impulse of each of the four digits dialed, the springs 231 are opened to interrupt the circuit over which R3I0 is being held energized, causing this relay to restore to open, at RA3I l, the loop circuit extending to the connector switch 26. At RA3I2 and RC3I4, the relay R3|0, upon restoring during the open circuit period of each impulse, opens the above-traced operating circuit for R4l0, but the latter relay, due to its slow-torelease characteristic, remains operated during impulsing. At the beginning of the rst impulse of each digit and when R310 restores, the previously mentioned circuit is completed for energizing the slow-acting relay R325, this circuit extending from ground at RA3I2 by way of RC3I3, C368, RA4I2. C364 and the winding of R325 to battery. 'Ihe relay R325 operates, when rst energized over the above traced circuit, and shortcircuits, at RA326 the branch of the loop circuit extending to the connector switch 26 which includes the upper winding of R320, the resistor 3I0 and the repeating transformer winding 354, thereby to reduce vthe resistance of the impulsing circuit by way of which impulses are repeated to the connector switch 26. Due to its slow-to-release characteristic, the relay R325 remains operated during each series of impulses dialed at the operators position 200. At the end of each digit dialed, the relay R3l0 remains operated for a sumcient time interval to permit the relay R325 to restore to open the above-mentioned shortcircuiting path. Also, at the end of each series of impulses, the shunt springs 238 are opened to interrupt the above-mentioned circuit for energizing R240. When R240 restores, it obviously recompletes the above-traced circuit for energizing the winding of R230 and the upper winding of R3I0 in Series, and opens the alternative circuit for energizing the signal lamp 205. This lamp is, however, maintained energized, due to the reoperation of R230. At the end of the dialing operation, the calling plug may, if desired, be withdrawn from the calling jack 203 for use in establishing other connections.

The apparatus embodied in the connector switch 26 responds to the impulses dialed at the operators position 200 and repeated thereto by the repeater 25 by selecting the called. line II and by selecting the type of ringing and the code of the ringing current to be used in signaling the called substation, all in the manner explained previously. The arrangement of the control apparatus embodied in the switch 26 is such that the called line is tested to determine the idle or busy condition thereof immediately the line selecting operation of the connector switch is completed. Busy-tone voltage is, however, not applied to the loop extending to the repeating transformer 350 until after the nal code selecting digit is dialed. If the called line is busy and busy-tone voltage is ultimately applied to the loop extending to the operated connector switch, the current owing over the loop causes an induced voltage to be impressed between the line con- .;,dictors of the trunk line I2 so that a busy-tone signal is generated by operation of the receiver included in the operators telephone set. On the other hand, if the selected called line is idle, ringing current of the selected code is projected over the line to signal the desired substation A and ring-back tone is impressed on the loop extending to the repeating transformer 350 and is transmitted by way of this transformer, the trunk line I2 and the transformer 250 to the receiver embodied in the operators telephone set, to indicate that the desired substation is being rung.

The desired conversational connection is completed when the call is answered at the substation'A. A direct current bridge is placed across the conductors of the line II when the call is answered, which causes the back bridge or battery reversing relay conventionally provided in the connector switch 26 to be energized. When this back bridge relay operates, the exchange battery is reversely connected to the line conductors of the link line 468 in the usual manner, so that the current traversing the upper winding of R320 is reversed, and the two windings of the last-mentioned relay are cumulatively energized. 'I'he relay R320 now operatesv to complete, at RA32I, an obvious circuit for energizing R3I5. The relay R3I5, upon operating, completes, at RA3I6 and RA3II, an alternative circuit for energizing the two windings of R3I0 in series. This circuit extends from battery at the upper terminal of the upper winding of R3I0 by way of the two windings of R3 I 0 in series, RA3 l 6, RABH, the resistor 308, RA306, th simplex circuit including the two sides of the trunk line I2, RA243, RC244, RA222, RC223 and the winding of R230 to ground. At RA3I1 and RC3I8, the relay R3I5 opens the original operating circuit for R3I0. The lower winding of R3I0 is a high resistance winding, such that, when serially included in the circuit by way of which the winding of R230 and the upper winding of R3I0 are energized, insufflcient energization is supplied to the relay R230' to maintain this relay operated. Thus, the relay R230 is caused to restore to open, at RA23I, the operating circuit for the signal lamp 205. The-deenergized condition of this lamp indicates that a talking connection is fully established.

After the desired connection to the substation A is` established, the operator may extend the same to a calling one of the lines terminating at the exchange I5 in the usual manner. Following the completion of the connection between the calling and called parties, the operator at the position 200 need not monitor the connection, but may disconnect her telephone set therefrom and rely upon the signal lamp 205 to indicate when the connection is cleared out at the called substation.

If the party who answers the call at the called substation A desires to resignal the operator without releasing the connection, he may do so by momentarily operating the switchhook provided at the called substation to open the loop circuit extending to the operated connector switch 26 and thus cause the momentary restoration of the back bridge relay embodied in this connector switch. When the back bridge relay of the operated connector switch restores, it reverses battery back over the loop extending to the repeating transformer 350 and in so doing reverses the direction of current flow through the upper wind- 1ng of R320, causing the last-mentioned relay to restore. Upon restoring, the relay R320 opens, at RA32I, the operating circuit for R3I5 and, when R3I5 restores, it removes the lower winding of R3I0 from the series circuit by way of which the relay R230 is energized. When the high resistance lower winding of R3I0 is removed from the series circuit noted, the relay R230 is sufllciently energized to operate and, upon operating, recompletes, at RA23I, the operating cir' cuit for the signal lamp 205. Obviously, when the back bridge relay embodied in the connector switch 26 reoperates to again reverse battery over the loop extending to the repeating transformer 350, the two relays R320 and R3I5 are caused to reoperate in the order named so that the lower winding of R3I0 is again serially included in the circuit including the upper winding of R3I0 and the winding of the relay R230. Thus, R230 is caused to restore to interrupt, at RA23 I, the circuit for energizing the signal lamp 205. The flashing of the lamp 205 indicates to4 the operator at the position 200 that she is being recalled by the party at the called substation A.

'I'he release -of the operated switch train is completely under the control of the operator at the position 200 after the call is answered by the operator. When the party at the called substation A hangs up, the back bridge relay embodied in the connector switch 261s caused to restore, in the manner pointed out above, to reverse battery back over the loop extending to the repeating transformer 350. Thus, the polarity iol of the current flowing through the upper winding A74 of R320 is reversed, and this relay is caused to restore to open the operating circuit for R3I5. When the relay R3I5 restores, it removes the lower winding of R3I0 from the series circuit including the winding of R230, causing the lastmentioned relay to reoperate to again complete the circuit for energizing the signal lamp 205. 'I'he continuous illumination of this lamp indicates that the connection'has been released at the called substation. The operator may now initiate the release of the established switch train by withdrawing the line connecting plug from the jack 20| to open, at the springs 228, the operating circuit for R220. Upon restoring, the relay R220 opens, at RA222 and RC223, the series circuit over which the two relays R230 and R3 I 0 are being held energized in series, causing both of these relays to restore. When the relay R230 restores, it opens, at RA23I, the circuit for energizing the signal lamp 205, and, when the relay R3I0 restores, it opens, at RA3I I, the loop circuit extending to the operated connector switch 26. Thus, the line and hold relays provided in the connector switch 26 are caused to restore to initiate the release of this switch and the finder switch 24. When the link is entirely released, certain of the relays provided in the connector switch 26 operate to mark the link as idle in the distributor 25', thus rendering the link available for use on other calls.

When the relay R3I0 restores, it recompletes, at RA3I2 and RC3I3, the above-traced operating circuit for R325 and interrupts, at RA3I2 and RC3I4, the above-traced circuit over which R4I0 is being held energized. When R4I0 restores, it opens, at RA4I2, the operating circuit for R325 and, at RA4I6, the operating circuit for R430. The momentary reoperation of R325 is without eifect; At RA4II, the relay R4I0 opens the above-traced circuit for energizing the lower winding of R320 and, at RA4I3 and RC4I4, it opens a point in the above-traced path for applying ground to the control conductor C361. Thus, the trunk line I2, and more particularly u the link line 468, is marked as idle in the con- 50 causing both of these relays to restore.

nector switches to which the last-mentioned line extends. The relay R430, upon restoring, opens, at RA435 and its associated working contact, the above-traced holding circuits for R400 and R450, At this is no longer present on the conductor C462 of the link line 468 so `that the relay R450 is not caused to reoperate. At RA43I and RA433, respectively, the relay R430 time, ground potential 55 opens the respective operating circuits for R460 and R440, causing both of these relays to restore. The relay R400, upon restoring, opens, at RA403 and RA404, a further point in its holding circuit and, at RA402, a point in the operating circuit of the relays illustrated in Figs. 3 and 4 are returned to their respective restored positions, and the repeater is conditioned for further use.v

As pointed out previously, if the connection as routed by way of the trunk line I2, the repeater illustrated in Figs. 3 and 4, and the finder switch 24, to the connector switch 26 is to be extended by way of one of the trunk lines extending between the exchange I0 and the exchange 30 to a line terminating at the lastmentioned exchange, the calling operator at the position 200 is only required to dial a single digit corresponding to the group of trunks noted. When this single digit is dialed, the connector switch 26 operates to seize a repeater associated with a preselected idle one of the trunk lines in the selected group. For example, if a trunk selecting digit is dialed at the operators position instead of the digits of the directory number identifying the substation A and the repeater 20 illustrated in Figs. 7 and 8 is seized by the connector switch 26, this connector switch operates to switch the callin loop circuit through to the repeater 20. When ,the link line 190 extending to the repeater 20 shown in Figs. 7 and 8 is seized by the connector switch 26, ground is supplied to the control conductor C165 to complete a circuit for energizing R150, this circuit extending by way of C165, RA1I8, RA121 and the winding of R150 to battery. When energized over this circuit, the relay R150 operates to complete, at RA155, an obvious holding circuit for itself. At RA154, the relay R150completes an obvious circuit for energizing the lower winding of R1 I0, which latter relay, upon operating, completes, at RA1I5 and RA1I6, an obvious holding circuit for itself. At RA1I0, the relay R1I0 completes an obvious circuit for energizing the slowto-release hold relay R120 and, at RA1I8, the relay R1I0 opens a point in the above-traced operating circuit for R150. At RA1I2 and RA1I4, the relay R1I0 opens a point in the circuit, traced hereinafter, for energizing the line relay R125. At RA1I6 and RC1I1, the relay R1I0 disconnects the line conductor\C164 from the upper terminal of the upper winding of R1I0. With the two relays R1I 0 and R150 operated, the loop circuit is extended to the repeating transformer 800 and the two relays R130 and R135 are energized in series thereover. More particularly, the circuit for` energizing R130 in series with R135 may be traced as extending from ground at the lower terminal of the winding of R130 by way ofthis winding, RC143, RA142, C115, the transformer winding 80|, C114, RA152, C110,

RA1 I2, RA1I I, C164, one side of the loop extendoperate when energized over this loop circuit,

but the polarity of the current traversing the circuit is such that the two windings of R320 are differentially energized and, hence, the relay R320 does not operate. Upon operating, the relay R130 prepares, at RA13I, a circuit, traced hereinafter, for energizing R140. The relay R135, upon operating, completes, at RA136 and its associated working contact, a circuit for energizing R840, this circuit extending from ground at RA83I by way of C180, RA136, C118 and the winding of R840 to battery. Upon operating, the relay R840 completes, at RA84I, a holding circuit for itself, which holding circuit extends from ground by way of the resistor 84I, RA84I, C180, RA136, C119 and the winding of R840 to battery. At RA842, the relay R840 completes an obvious circuit for. energizing the slowacting relay R820, which latter relay, upon operating, completes, at RA825, an obvious circuit for energizing R830. The relay R820, upon operating, also completes, at RA826, a path for applying ground to the control conductor C165, this path extending from ground at RA109 by Way of C189, RA826, C188 and RA155 to the switches in the exchange 10 from releasing and also to prevent the operated relays R110, R120,

R130, R135 and R150 from restoring. At RA824, the relay R820 prepares a priming circuit, traced hereinafter, for energizing the pulse responsive relay R135. At RA821 and RC823, the relay R820 completes a loop circuit including the line conductors C882 and C883 of the trunk 13 between the repeating transformer 800 and the two-way repeater 885 associated with the distant end of the trunk line and located in the exchange 30. As indicated above, the repeater 885 is identical in all respects with the repeater shown in Figs. 7 and 8 and the completion of the above-mentioned loop circuit results in the operation of certain of the relays provided therein, which relays, upon operating, cause one of the finder switches in the exchange 30 to seize the repeater 885 and to extend the calling loop circuit to an associated one of the numerical switches embodied in the exchange. More particularly, when the loop circuit is extended to the repeater 885, the windings of the line relay embodied therein and corresponding to R shown in Fig. '1 are energized over the loop circuit in series with the winding of R810 and the lower winding of R815. One of the finder switches embodied in the exchange 30 is caused to operate to seize the repeater 885 in response to the operation of the line relay embodied in this repeater. After the loop circuit is switched through to one of the connector switches in the exchange 30, the winding of R810 and the lower winding of R815 are held energized in series with the respective windings of two line relays embodied in the seized connector switch. 'I'he relay R810, upon operating, opens, at RA811, a point in the circuit, traced hereinafter, for energizing R104. Shortly after the relay R810 operates, the relay R838, which is energized in response to the operation of R820, operates to complete, at RA831 and its associated working contact an obvious circuit for energizing the upper winding of R815. The two windings of R815 are now differentially energized and, consequently, this relay does; not operate. The relay R815 operates only when its two windings are cumulatively energized. The relay R830, upon operating, opens, at RA831 and its associated resting contact, a point in the operating circuit, traced above, for R840. At RA832, the relay R830 prepares a point in the above-mentioned operating circuit for R104 and, at RA833, it completes a multiple path for holding ground on the control conductor C165, this multiple path extending from ground at RA109' or, the lower terminal of the lower winding of the impedance element 103, by way of C189, R833, C188 and RA155 to thecontrol conductor noted.

As explained previously, the switching equipment provided in the exchange 30 is substantially a duplication of that shown in Fig. 5 and disclosed in the above-referred to copending application in so far as the automatic switches are concerned. When, therefore, the calling loop circuit is extended by way of the repeater 885 and one of the finder switches in the exchange 30 to the connector switch associated with the operated finder switch, the seized connector switch isconditioned to respond to impulses transmitted thereto in response to further opera.. tion of the impulsing device provided at the operators position 200.

Impulses produced by further operation of the impulsing device 204 provided at the operators position 200 are repeated by the repeater 25 shown in Figs. 3 and 4 and through the established switch train comprising the finder 24 and the connector switch 26 to the repeater 20 illustrated in Figs. 1 and 8. At the beginning of the first impulse of the second digit dialed at the operators position and when R310 restores to open the loop circuit extending through to the repeater 20 shown in Figs. 7 and 8, the relay R135, which is being held energized over this loop `cuit, restores to complete, at RA136 and its associated resting contact, a priming circuit for itself, which priming circuit extends from ground by way of the resistor 841', RA841, C180, RA136, C181, RA824, C182, the resistor 141 and the winding of R to battery. Due to the resistance of the two resistance elements 841' and 141, the eurent traversing this priming circuit is insufficient to cause the reoperation of R135. Upon restoring, the relay R135 alsointerrupts, at RA136 and its associated working contact, the above-traced holding circuit for R840, causing the last-mentioned relay to restore. At RA841, the relay R840, upon restoring, opens the above-traced priming circuit for R135 and, at RA842, it opens a point in the operating circuit for R820. At RA843 and RC845, the relay R840, upon restoring, completes a circuit for energizing the slow-acting relay R865, this circuit extending from ground at RA831 by way of RA843, RC845, and the winding of R865 to battery. At RA846, the relay R840 completes a circuit extending from ground at RA831 and by way of RA853 for energizing the upper winding of R860. At RA841, the relay R840v opens a point in a circuit, traced hereinafter, for energizing the lower winding of R850. The slow-acting relay R865, upon operating, completes, at RA868, an obvious circuit for energizing the slow-to-release relay R815. At RA866, the relay R865 completes a path extending by way of C112 for short-circuiting the winding of R130, thereby to remove the resistance of this winding from the calling loop circuit for the purpose of improving the impulsing characteristics of the calling loop circuit. At RA861, the relay R865 short-circuits the series circuit including the winding of R810, the lower winding of R815 and the windings 803 and 804 of the repeating transformer 800, thereby to reduce the resistance of the loop circuit extending to the operated connector switch located in the distant exchange 30. At RA869, the relay R865 completes a circuit for energizing the relay R160, this circuit extending from ground at RA831 by way of RA869, C184 and the winding of R160 to battery.

The relay R815, upon operating, opens at RA811 a point in the circuit, traced hereinafter, for energizing the lower winding of R104 and completes, at RA816, an obvious circuit for energizing the slow-to-release relay R880 which latter relay operates to open at RA881 a further point in the circuit for energizing R104. The relay R160, upon operating, completes a holding circuit for itself, which circuit extends from ground at RA831 by way of C185, RA162 and the winding of R to battery. At RA161, the relay R160 prepares a circuit, traced hereinafter, for energizing R140.`

The relay R860 operates, when R840 restores to complete the above-traced circuit for energizing the upper winding of R860, and,=upon operating, completes, at RA863, an obvious path for short-circuiting its lower winding, thereby to render itself slow to release. At RA862, the

relay R860 completes an obvious holding circuit for the slow-acting relay R820. At RA884, the relay R860 completes the above-mentioned circuit for energizing the lower winding of R850, this circuit extending from ground at RA83I by way of RA864, RA8411` and the lower winding of R850 to battery. Since the upper winding of R850 is normally short-circuited through the armature RA852, this relay is slow to operate. When the relay R850 operates it prepares, at RA85I, the above-traced operating circuit for R840 and opens, at RA853, the above-traced operating circuit for R860. At RA854, the relay R850 completes a locking circuit for itself, which circuit extends from ground at RA88I by way of RA854, RA841 and the lower winding of R850 to battery. At RA852, the relay R850 opens the path short-circuiting its upper winding and, at RA853, it opens the above-traced operating circuit for R860. At RA85I, the relay R850 completes an alternative priming circuit for R135, this circuit extending by way of C180, RA138, C18I RA824, C182, the resistor 141 and the-winding of R135 to battery. Due to the resistance of the resistor 141, the relay R135 does not operate when energized over this alternative priming circuit, but is conditioned to be fast to operate when the calling loop circuit is subsequently recompleted at the end of the open circuit period of the impulse. An interval following the operation of R850, the relay R860 restores to open, at RA864, a point in the aboveftraced operating circuit for R850. At RA862, the relay R860 opens the above-traced holding circuit for R820 and, at RA883, the relay R860 opens the path shortcircuiting its own lower winding.

The relay R850 remains operated until the open circuit period of the first impulse is ended, at which time R135 is again energized over the calling loop circuit. Upon reoperating, the relay R135 opens, at RA136 and its associated resting contact, its alternative priming circuit as traced above and recompletes, at RA136 and its associated working contact, the above-traced operating circuit for R840. The last-mentioned relay, upon reoperating, opens, at RA841, a point in the above-traced holding circuit for R850 and opens, at RA846, a point in the above-traced operating circuit for R860. At RA843 and RC845, the relay R840 opens the above-traced operating circuit for R865 and, at RA843 and RC844, prepares the operating circuit, traced hereinafter, for R104, which latter circuit is now held open at RA811 and RA88I. Shortly following'the reoperation of R840, the relay R850 restores to open, at RA854, a further point in its holding circuit and to close, at RA853, a point in the operating circuit for R860. At RA85I, the relay R850, upon restoring, opens a point in the operating circuit for R840, which latter relay is now held energized over its holding circuit as traced above and extending by way of the resistor 84|' and RA84I.

At the beginning of the open circuit period of the second impulse, the relays R135 and R840 restore, in the order named and in the manner just described, whereby the sequential operation of R860 and R850 followed by the restoration of' R860 is repeated. At the end of the open circuit period of the second impulse, when the two relays R135 and R840 reoperate, the relay R850 again restores. During each succeeding impulse of the series, the above-described sequence of operations is repeated, it being pointed out that the relay R865, due to its slow-to-release characteristlc, remains operated throughout the series of impulses and only restores at the end of the digit, at which time R840 is held operated for a period of time exceeding the period required for restoration of the relay R865. Each time the relay R865 operates to short-circuit, at RA861, the series circuit including the winding of the relay R8I0, the latter relay is deenergized and restores to prepare at RA8II a point in the above-mentioned circuit for energizing R104. 'I'he circuit for energizing R104 is, however, held open during impulsing by the two operated relays R815 and R880. As indicated above, at the end of each series of impulses the slow-acting relay R885 restores to open, at RA866, the path shortcircuiting the winding of R130, permitting the latter relay to reoperate. At RA861, the relay R865, upon restoring, opensthe path shunting the series circuit including the two windings 803 and 804, the winding of R8 I 0 'and the lower winding of R8I5, causing the relay R8I0 to reoperate and open, at RA8II, the circuit for energizing R104 before the two slow-to-release relays R815 and R880 fall back. At RA868 the relay R865 opens a point in the above-traced operating circuit for R160. `At RA868, the relay R865 interrupts the operating circuit for R815, causing R815 and R880 to restore in the order named to reprepare the operating circuit for R104. It will be apparent from the foregoing description that the relation between the period of deenerthis relay and theslow-to-operate characteristic of R850.

During each impulse of each digit, the relay R860 opens, at RA88I, a point in the loop circuit extending by way of the trunk line I3, the repeater 885 terminating the distant end of this trunk line, and the operated nder switch in the exchange 80 to the connector switch associated with the operated nder switch. The connector switch into which the impulses are delivered responds in t e manner pointed out above with reference to, the switching apparatus illustrated in Fig. 5. More particularly if the desired connection is to be routed by way of the operated connector switch'in the exchange 30 and one of the trunk lines extending to the manual oillce 40, a single digit is dialed. The connector switch responds to the digit by seizing a previously assigned idle one of the trunk lines' extending to the manual oflice, or, more particularly, a twoway repeater terminating an idle trunk line, extending to the manual oillce 40 and switches the calling loop circuit through thereto. On the other hand, if the connection is to be routed to one of the subscribers having a substation associated with one of the lines terminating at the exchange 80, four additional digits are dialed at the operators position 200, the impuulses of which are repeated by the repeater illustrated in Figs. 7 and 8 to the operated connector switch in the exchange 80. This connector switch responds to the impulses to select the desired called line and the code of the ringing current corresponding to the desired substation on the called line.

If the connection is routed to a subscribers line terminating at the exchange 30 and the line is found busy at the time it is selected by the operated connector switch having access thereto, busy tone is returned over the trunk line I3 and by way of the repeater illustratd in Figs. 7 and 8, the established switch train in the exchange I0, the repeater illustrated in Figs. 3 and 4, and the trunk line I2 to the operators position 200. In the event the selected called line is idle and ringing current is projected thereover to signal the desired substation, ring-back tone is delivered over the partially established communication connection to the operators position to indicate that the desired called substation is being rung.

Assuming the connection is extended to the substation B, the desired conversational circuit is completed when the call is answered at this substation. When the call is answered, the back bridge relay or called party answer relay embodied in the operated connector switch located in the exchange 30 operates to reverse battery back over the trunk line I3, thereby to reverse the direction of current flow through the Winding of R8I0 and the lower winding of R8I5. The relay R8I5 is now cumulatively energized and operates to complete, at RASIG, the above-mentioned circuit for energizing R140, which circuit extends from ground at RA83I by way of C185, RA13I, C186, RA8IG, C183, RA16I and the winding of R140 to battery. When energized over this circuit, the relay R140 operates its armatures RA14I and RA144 into engagement with their respective associated armature springs RA142 and RA145, thereby to reverse battery back over the loop extending to the repeater illustrated in Figs. 3 and 4. The reversal of battery over the loop extending to the last-mentioned repeater causes the relay R320 to operate in the manner pointed out above, which relay, upon operating, completes the operating circuit for R3I5. When the relay R3I5 operates, it includes the high resistance lower winding of R3 I0 in the series circuit by way of which the relay R230 provided at the operators position 200 is energized, causing the last-mentioned relay to restore. The relay R230, upon restoring, opens the circuit for energizing the signal lamp 205 and this lamp is darkened to indicate that the desired connection is fully completed. During the interval when the called substation B is being rung or after the call is answered, the operator located at the operators position 200 may extend the connection back to a calling one of the lines terminating at the exchange I in the usual manner and rely upon the signal lamp 205 to indicate when the connection is to be released. In this regard it is pointed out that the entire switch train by Way of which the connection is routed to the called substation B is held operated until the operator at the operators position withdraws the line connecting plug from the jack Hence, if the answering party at the called substation B desires to recall the operator at the operators position 200, he may operate the switch hook at the called substation up and down one or more times to cause the signal lamp 205 to flash, without any danger of releasing the operated switch train.

More particularly, each time the called party momentarily operates the switch hook at the called substation B to its normal position, the loop circuit extending to the called substation is opened for a short interval and the back bridge relay embodied in the operated connector switch located in the exchange 30 restores for a short period to reverse battery back over the loop extending to the repeater 20 illustrated in Figs. I and 8., The momentary reversal of battery over the last-mentioned loop causes the relay R8I5 to be differentially energized and this relay restores for a short period. Upon restoring, the relay R8 I 5 opens, at RA8I6, the above-traced operating circuit for R140, which latter relay restores to reverse battery back over the loop extending to the repeater illustrated in Figs. 3 and 4. Obviously, when R8 I 5 reoperates, the relay R140 reopcrates to again reverse battery over the loop extending to the repeater 25. During the interval when R140 is restored, the relay R320 is differentially energized and restores to open the operating circuit for R3I5, causing the latter relay to restore and remove the high resistance lower winding of R3I0 from the series circuit over which R230 is energized. Hence, R230 is caused momentarily to reoperate to complete, at RA23I, the circuit for energizing the signal lamp 205. The ashing of the signal lamp 205 indicates to the operator that she is being recalled by the called party at the substation B.

When the called party at the substation B hangs up at the end of the conversation, the loop circuit extending to the called substation is interrupted to cause the sequential restoration of R8I5, R140, R320 and R3I5 in the manner just described. When R3I5 restores, the lower winding of R3I0 is removed from the circuit over which R230 is energized and the last-mentioned relay reoperates to recomplete the circuit for energizing the signal lamp 205. Continuous illumination of the lamp 205 indicates that the connection has been cleared out at the called substation. When the operator at the operators position 200 withdraws her line connecting plug from the jack 204, the relay R220 restores, in the manner pointed out above, to open the circuit over which R230 and the upper winding of R3I0 are being held energized in series, causing both of these relays to restore. When the relay R3I0 restores, the loop circuit extending through the operated switch train in the exchange I0 to the repeater 20, illustrated in Figs. 7 and 8, is opened, causing the two relays R130 and R135 to restore. When R130 falls back it opens, at RA13I, the operating circuit for R140, causing the latter relay to restore. The relay R135, upon restoring, opens, at RA136, the holding circuit for R840. When the relay R840 falls back, it opens, at RA842, the operating circuit for R820 and recompletes, at RA843 and RC845, the operating circuit for R865. Upon operating, the relay R865 completes, at RA868, the operating circuit for R815, thereby to cause the sequential operation of R815 and R880. At RA846, the relay R840 completes the above-traced operating circuit for R860, which latter relay, upon operating, opens, at RA86I, the loop circuit extending to the operated switch train in the exchange 30. When R860 operates, it completes, at RA864, the operating circuit for R850 and, at RA862, the holding circuit for R820. Shortly thereafter, the relay R850 operates to open, at RA853, the operating circuit for R860 and to complete its holding circuit. When R860 restores, it opens the holding circuit for R820 permitting the last-mentioned relay to fall back, after an interval, to open the operating circuit for R830. When R830 restores, itL opens the operating and holding circuits for R850. R860. R865 and R160, causing the operated ,R8|0, causing the last-mentioned relay to restore,

- and when R865 thereafter restores the loop circuit over which the winding of R8l0 is energized is open at RA82|,and RC823 so that R8I0 does not reoperate. At RA868, the relay R865 opens the operating circuit for R815, thereby to cause the sequential restoration of this relay and the relay R880. When the relay R860 reoperates, in the manner just described, it opens, at RA86| and RC823. a point in the loop circuit extending between the repeater illustrated in Figs. 7 and 8 and the operated switch train in the automatic exchange 30. Also, when the relay R820 i'alls back, a further point is opened in this loop circuit so that the operated switch train in the exchange 30 is permitted to release in the manner described above with reference to the apparatus illustrated in Fig. 5. When the two relays R820 and R830 restore, the two paths, traced previously, for applying ground to the control conductor C165 are opened, and the holding circuits for R1i0 and R150 are interrupted,causing the two last-named relays to restore. When ground is removed from the control conductor C165, the operated switch train in the exchange I and including the two switches 24 and 26 is permitted to release in the manner described above. During the release of the operated switch train in the exchange I0, ground is removed from the control conductor C361. Thus, the connection is entirely released and the switching apparatus involved therein is conditioned for further use.

The arrangement of the repeater illustrated in Figs. 7 and 8 is such that this repeater and the preceding switch train in the exchange l0 are held operated until after the operated switch train in the exchange 30 is released. Thus, so long as the loop circuit extending to the called substation is complete, the battery reversing relay provided in the operated link in the exchange 30 is energized and battery potential is extended to C882 through the winding of one of the line relays embodied in the operated link in the exchange 30. Hence, when the relay R820 is caused to restore in response to the release of the connection at the calling end thereof and in the manner just described` it completes a circuit for energizing the relay R810 in series with the line relay embodied in the operated link in the exchange 30 from which battery potential on C882 is derived. This circuit extends from ground by way of the winding of R810, C11I, RA15I, C113, RC822, RA82I, RA86I, C882 and the winding of the line relay noted to battery. 'Ihe energization of this line relay is insuicient to hold the relay operated so that the operated switch train in the exchange 30 is not prevented from releasing. The relay R810 operates when energized over the circuit just traced and completes at RA81| an obvious holding circuit for R830. With R830 operated the repeater illustrated in Figs. 7 and 8 and the switch train in the exchange l0 are held operated until the operated switches in the exchange 30 are released. at which time the circuit over which R810 is being held energized is interrupted. When R810 restores it opens the holding circuit for R830 causing the latter relay to restore to cause the full release of the repeater illustrated in Figs. '7 and 8 and the operated link in the exchange i0 in the manner set forth previously. If the connection is cleared out at the called substation before the calling party hangs up, the battery reversing relay provided in the operated connector switch in the exchange 30 is restored and, hence, ground potential is present on C882 so that no circuit for energizing R810 iscompleted in response to the restoration of R820. Thus, the release o f the repeater illustrated in Figs. '7 and 8 is not iniluenced by the relay R810.

Referring now more particularly to the operation of the repeater 25, illustrated in Figs. 3 and 4, to route a connection tothe operator's position 200 in response to the seizure thereof by one of the connector switches embodied in the exchange I0 and assuming that the call to the manual oilce I is initiated at the substation A, and, further, that the connection is routed by way of the finder switch 24 and the connector switch 26, when the last-mentioned switch operates to seize the link line 468 extending to the repeater, the calling loop circuit is switched through thereto and ground is impressed upon the control conductor C361. The ground potential impressed upon C361 results in the energize.- tion of R330 over a circuit extending by way of C361 RA4I3, RC4i5, C366 and the winding of R330 to battery. When energized over this circuit, the relay R330 operates to complete, at RA338, a holding circuit for itself, which circuit extends by way of the grounded conductor C361, RA338 and the winding of R330 to battery. At RA332, the relay R330 completes a circuit extending by Way of C359 for energizing R450. At RA33 I, the relay R330 prepares the loop circuit to the repeating transformer 350 and, at RA333 and RA336, connects the winding of R345 to be energized by way of the last-mentioned loop circuit. At RA331, the relay R330 closes a point in the path, traced hereinafter, for impressing paystation-tone voltage across the line conductors C351 and C358. The relay R450, upon operating, opens, at RA454, the previously-traced path for impressing busy tone upon the loop extending to the operator's position 200 when an all-linksbusy condition exists. At RA458, the relay R450 opens a point in one path for applying ground to the tone apparatus start conductor. At RA459, the relay R450 opens a point in the path for applying ground to the tens relay control conductor and, at RA450, it opens a point in the path for connecting the start conductor C461 to the unit relay control conductor C466, thereby to prevent a finder-connector link in the exchange I0 from operating when the relay R430 is subsequently caused to operate. At RA45I and RA452, the relay R450 extends the calling loop circuit to the repeating transformer 350, thereby to cause the energization and operation of the relay R345. More particularly, the last-mentioned relay is energized over a circuit extending from ground at RA43I by way of the line balancing impedance element 409, C360, RA336, the winding 354, C351, RA452, RA45I, C462 and the correspondingl side of the loop extending to the calling substation, the bridge connected between the line conductors of the calling line at the calling substation, the opposite side of the loop extending to the calling substation, C358, RA33I, the winding 353, RA333, RC335 and the winding of R345 to battery. Upon operating, the relay R345 completes, at RA346 and RA341, respectively, circuits for energizing the two relays R3i5 and R340, respectively. At RA348, the relay R345 completes a circuit extending by way of RA303 for energizing the slow-to-operate relay R305. The relay 

